No abstract

Spectroscopic ellipsometry measurements have been performed during the preparation of hydrogenated amorphous silicon p-i-n solar cells in the SnO2:F/p-i-n/Cr configuration. Postdeposition data analysis yields the evolution of bulk, surface roughness, and interface layer thicknesses with ∼0.2 Å sensitivity. In addition, the dielectric functions and optical gaps of the p-, i-, and n-layers are determined in the analysis. With the real time measurement approach, the layer properties are determined in the actual device configuration, rather than being inferred indirectly from studies of thick film counterparts.

The mixed crystal Rb & "(NH4)"HzAs04 of ferroelectric RbH&As04 and antiferroelectric NH4HzAs04 has been investigated for several values of x by measuring the dielectric constant along the a and c axis in the temperature range from 30 to 200 K. The phase boundary between the ferroelectric phase and the proton glass state is found to be between 0.13 and 0.20, and a similar boundary between the proton glass state and the antiferroelectric phase is observed to be located between 0.44 and 0.49. For samples with 0.23~x~0.44, the dielectric data can be scaled using the Vogel-Fulcher law with a static freezing temperature To. From our experimental results, we construct a phase diagram of Rb, "(NH4)"H&As04.

Real time spectroellipsometry (RTSE) has been applied to study the growth of a-Si1-xCx:H alloys (x∼0.1; Eg=1.90–2.00 eV) for applications as i- and p-type layers in wide band gap solar cells. Two important material parameters, the optical gap and the relative bond-packing density (or void volume fraction), can be estimated from RTSE data collected during the growth of a sequence of layers onto the same substrate using different plasma-enhanced CVD conditions. In this way, large regions of parameter space have been scanned expeditiously, and an improved understanding of the effects of H2-dilution, substrate temperature (Ts), plasma power, gas pressure, and gas flow on the film properties has been obtained.

We have applied real time spectroscopie ellipsometry (RTSE) to monitor the successive growth of p-type a-Si1-xCx:H and i-type a-Si:H on specular SnO2:F (i.e., the superstrate solar cell configuration) in a single-chamber deposition system. Both the microstructural evolution, which includes the surface roughness and bulk layer thicknesses versus time and bulk layer void volume fraction, as well as the optical properties, which include the dielectric function (1.5–4.0 eV) and optical gap of the individual layers, were determined from RTSE data collected during growth. The accuracy of our approach is demonstrated by correlating structural parameters obtained both by RTSE and atomic force microscopy. Based on prior information deduced by RTSE, the TCO/p/i structure was fabricated with optimized procedures that have sought to minimize TCO/'p and p/i interfacial problems. These studies illustrate that RTSE can be a valuable tool for identifying problems in the fabrication of a-Si:H solar cells and ultimately improving cell performance.